Dense fluid spray cleaning process and apparatus

ABSTRACT

Disclosed is a dense fluid spray cleaning apparatus comprising a gas supply ( 3 ) for providing a predetermined amount of a gas to an enhanced joule-thompson condensation reactor ( 2 ) and for providing gas to a propellant generator ( 4 ), a premix chamber ( 6 ) for receiving a solid particulate from the enhanced joule thompson condensation reactor and heated gas from the propellant generator, and a mixing chamber ( 8 ) for receiving the solid particulate and the heated gas and producing a spray stream containing the solid particulate.

BACKGROUND OF INVENTION

Carbon dioxide exists as a low-density gas at standard temperature andpressure conditions and possesses phase boundaries with a triple point(Solid-Liquid-Gas co-exist in equilibrium like a glass of ice cubes andwater) and a critical point (Liquid-Gas have identical molar volumes).Through pressure or temperature modification, carbon dioxide can becompressed into a dense gas state. The term ‘Dense Phase Carbon Dioxide’is used herein to describe all phases of carbon dioxide: liquid state,supercritical state, dense gas state, and solid-state. These states havedensities that are within the range of liquid-like or near-liquidsubstances.

Compressing carbon dioxide at a temperature below its criticaltemperature (C.T.) liquefies the gas at approximately 70 atm. Coolingliquid-state or gas-state carbon dioxide to its freezing point causes aphase transition into solid-state carbon dioxide. Compressing carbondioxide at or above its critical temperature and critical pressure(C.P.) also increases its density to a liquid-like state, however thereis a significant difference between compression below and above thecritical point.

Compressing carbon dioxide above its critical point does not effect aphase change. In fact, carbon dioxide at a temperature at or above 305 K(88 F) cannot be liquefied at any pressure, yet the density for the gasmay be liquid-like. At the critical point the density is approximately0.47 g/ml. At or above this point carbon dioxide is termed asupercritical fluid (SCF). Supercritical carbon dioxide can becompressed to a range of liquid-like densities, yet it will retain thediffusivity of a gas. Continued compression of supercritical carbondioxide causes continued increase in density, approaching that of itsliquid phase.

Solid-state carbon dioxide is useful for removing particulates and traceorganic residues from surfaces, using a process typically called SnowCleaning or Snow Departiculation. Similar to liquid and supercriticalfluid cleaning agents, solid-state carbon dioxide's cleaning power canalso be described in both physical and chemical terms. The process ofsnow departiculation can be described as a kinetic energy transferprocess called “Linear Momentum Transfer” in accordance with thefollowing vector quantity:

P=MV, where

P—Linear Momentum of Solid Carbon Dioxide Particle or Surface Particle

M—Mass of Solid Carbon Dioxide Particle or Surface Particle

V—Velocity of Solid Carbon Dioxide Particle or Surface Particle

A stream of solid carbon dioxide particles having significant mass andvelocity impact a stationary surface particle causing the surfaceparticle with a given mass to accelerate away from the surface to agiven velocity in accordance with the following equation:V _(sp)=(M _(cp) /M _(sp))V _(cp), where

V_(sp)—Velocity of Surface Particle

M_(cp)—Mass of Carbon Dioxide Particle

M_(sp)—Mass of Surface Particle

V_(cp)—Velocity of Carbon Dioxide Particle

The physical energy transferred during a snow departiculation process isusually sufficient to overcome strong electrostatic and intermolecularadhesive forces, commonly referred to as Van der Waal's forces, thathold small particles to the surface.

The mechanism for the removal of trace organic films using snow is notfully understood, but has been postulated to be a combination ofmomentum transfer and a phase change of minute solid carbon dioxideparticles from solid-state to liquid-state (compression) and subsequentsolutioning of trace surface residues. According to the phase diagramfor carbon dioxide, a minimum impact compression of approximately 6 atm(88 psi) at 195 K is required to produce a liquid interphase. Energytransformations are possible other than the formation of a liquid phase,including particle fragmentation or shearing, gas phase transition(sublimation), and temperature rise in the solid (thermal energy) atimpact.

Solid carbon dioxide is being used in a number of commercial productcleaning applications to remove trace organic and inorganic residues andparticulates. Liquid carbon dioxide is rapidly expanded (joule-thompsonexpansion) through an orifice of a valve to form a mixture of subcooledgas state and solid state carbon dioxide—referred to as “snow” or “dryice”.

Solid carbon dioxide is applied in conventional applicators according totwo types of applicators, described as Type I and Type II snow cleaningapplicators as follows:

Type I Snow Applicator: Liquid carbon dioxide, stored in a high pressurebottle, is expanded from 850 psi at 298 K through a suitable nozzle intogas state (the propellant) and solid state carbon dioxide (the cleaningagent) and directed at a substrate. Conventional Type I applicators arecommonly used in precision cleaning applications at close proximity to asubstrate and have relatively simple operation and low-cost designs.

Type II Snow Applicator: Liquid carbon dioxide is first expanded intosolid carbon dioxide using a suitable “dry ice machine”, packed into drypellets of uniform size, or shaved into a powder, and then fed into aspray apparatus using compressed air to propel the solid carbon dioxidefrom a spray nozzle. The air and solid mixture impacts the surface. AType II applicator is typically used for cleaning large rigid structuresbecause of its more aggressive action at close proximity (i.e., forcoating removal) and long-range particle cleaning action (large and hardsnow pellets). However, Type II equipment and operational costs aresignificantly higher than Type I systems.

Type I and Type II applicators include:

1. Fixed position applicators

2. Pistol grip applicators

Conventional applicators are designed to have a single spray pattern,with various interchangeable nozzle designs for different substrates andsurface cleaning applications. Type II designs can also vary impactenergy through control of compressed air pressure whereas Type I designscannot. Disadvantages associated with these mechanical designs include:

-   -   1. Fixed spray pattern.    -   2. Non-interchangeability of applicator designs        (fixed<−>handheld<−>robotic).    -   3. Bulky configurations.    -   4. Uncontrolled tribocharging (electrostatic buildup) of        non-metallic substrates such as plastics.    -   5. Rapid localized substrate cooling and subsequent deposition        of contaminating residues.    -   6. Ineffective deep hole cleaning.    -   7. Expensive equipment costs.

Conventional snow cleaning applicators (Type I and II) suffer from thefollowing disadvantages:

-   -   1. Impact energy and the amount of snow particles available at        the surface decreases as the distance from the expansion valve        to the applicator nozzle increases. Type I applicators must have        an expansion valve located close to the nozzle and the nozzle        must also be very close to the substrate to effectively remove        residues.    -   2. Entrainment of ambient air which often contains moisture,        particles, and other contaminating residues which condense onto        surfaces which have been supercooled by the snow particle/gas        stream.    -   3. Externally applied environmental control measures such as        heated air and particle control hinder the cleaning performance        and are applied so generally that localized condensation,        particle entrapment, or tribocharging still occur. Conventional        applications employ macro-environmental control (clean rooms,        infrared heaters etc.) measures. Type I snow applicators cannot        be used in relatively uncontrolled environments.    -   4. The process of expanding liquid carbon dioxide into solid        state and subsequent contact of solid state carbon dioxide with        surfaces causes a phenomenon called tribocharging, whereas the        solid carbon dioxide (primary dielectric) builds electrostatic        charge of up to 5 to 15 mJ at 10 KV to 20 KV as it contacts a        substrate (secondary dielectric). This type of electrical charge        build-up can be extremely damaging to microelectromechanical        devices (or can induce latent ESD defects) and will cause a        departiculated surface to become an attractor (magnets) of        airborne particles following snow cleaning operations.        Electrostatic effects can be caused through direct contact of        charged solid carbon dioxide particles with the substrate which        causes a discharge event or current flow through the surface        (direct discharge) or may be caused through electrostatic field        exposure and subsequent charging of the surface (induced        charging).    -   5. In many applications, spray cleaning is performed independent        of and prior to operations such as microwelding, adhesive        bonding and thermal curing and soldering. Moreover, following        production operations such as CMP the substrate is wet with        aqueous residues and must be dried prior to snow cleaning        operations. A method and apparatus is needed to serve as an        integrated simultaneous drying, cleaning and production tool.    -   6. Xenon flashlamp technology is used with solid carbon dioxide        (Type II) to remove old paint from aircraft surfaces. This type        of technology uses an intense UV radiation (not a laser) burst        to pyrolize substrates which produces a large amount of heating        radiation as a by-product. The pyrolized paint is swept away        from the substrate using a flow of carbon dioxide pellets. This        technology is large and bulky and cannot be used to precisely        clean small parts commonly found in the semiconductor,        electrooptical and electronics markets. A precision coherent        photon-based technique is needed to remove small contaminants        from intricate assemblies.    -   7. In some applications, solid phase carbon dioxide chemistry        requires physicochemical modification to provide enhanced        separation and surface finishing capabilities. To date, no        effective technique has been demonstrated to accomplish this        requirement.    -   8. Type II applicators also suffer from being too aggressive        (i.e., substrate damage), very noisy, bulky and too costly for        most precision substrate cleaning applications.    -   9. Conventional snow cleaning applicators do not lend themselves        to integration with production processes such as stamping,        welding, bonding, curing and abrasive surface finishing        operations because of the aforementioned problems discussed        above.

Conventional snow cleaning processes do not have a method for real-timeanalysis of cleaned surfaces to accept or reject a particular cleaningoperation. This is especially advantageous for in-line continuousquality control monitoring of surface cleaning performance.

Conventional ESD Control Methods used with Solid Carbon Dioxide:

Air Ionization—air is ionized using a DC or AC ionizer that is thenflushed over an affected surface. The problem with this approach is thatflowing air induces contamination through introduction of humidified airand potential particles. Also ionizing air impingement requires floodingthe surfaces to be cleaned. This process can subtract from the cleaningenergy. Moreover, the charges present within the structure of thecleaning agent are not reduced effectively using this technique.

U.S. Pat. No. 5,409,418 proposes a nozzle-mounted secondary gas ionizerwhich surrounds the snow stream with oppositely charged ions duringimpingement. U.S. Pat. No. 5,725,154 proposes neutralizing chargesduring snow cleaning following each cleaning pulse with a separatepropellant gas neutralization pulse.

Most prior art suffers from these typical drawbacks:

-   -   Impossible to precisely control charges being delivered to a        substrate—each substrate and atmosphere is different.    -   The portion of a substrate being impacted by the sublimable        cleaning agent is not affected by neutralizing ions—only the        circumference of the snow spray is affected.    -   Backside or nearby electrostatic charging due to electric fields        is not affected by these techniques—electric fields pervade the        materials creating complexly charged surfaces.

Nuclear Ionization—the substrate is exposed to radioactive particles(alpha). This process is line-of-sight and very short range.Obstructions of the smallest variety will eliminate beneficialionization using this technique.

Fong '786, referenced herein, uses nuclear ionization to reduceaccumulated electrostatic charges contained on solid carbon dioxidestored and mixed within a storage hopper and prior to and duringdelivery into a high pressure feed line. Fong '786 suffers from all ofthe drawbacks cited above.

Grounding—the substrate in grounded to earth using a suitable resistorto bleed charges at an acceptable rate. The main problem with thisapproach is that the electrostatic charge and electrical overstress arenot effectively controlled on non-conductive substrates.

Antistatic Chemicals—this approach is the most effective on preventingcharge creation by the cleaning agent. However this method tends to, byitself, become a source of chemical contamination within the cleaningprocess. To date no use of antistats within cryogenic cleaning agents isknown

Moreover, in cleaning quartz lenses, as well as many othernon-conductive substrates it is difficult to control electrostaticcharging of the quartz substrate during sublimable spray cleaning.Flooding the surfaces with ionized air only works prior to and followingsnow cleaning. During snow cleaning, as much as 2000 volts ofelectricity of positive and negative charge can be created following thesnow-surface tribocharging contact event. Contaminants such as particlestend to move in relationship to thermal and electric fieldgradients—both of which are present in snow cleaning.

The backside of the quartz is typically opposite in charge (conservationof charge) during snow cleaning, therefore the particles once liftedfrom a front surface migrate around the substrate within a thin-film ofsubcooled atmosphere and become attracted to the oppositely chargedsurface on the backside. Quartz cannot be grounded and commonly usedantistatic chemical agents contained in the cryogenic cleaning agentwould leave stains during cleaning.

A photoelectric effect has been advantageously employed in differentarts for decades. In certain commercial ionization applications, thephotoelectric effect is used to produce highly energetic photons from0.13 to 0.41 nm (9.5 to 3 KeV) to ionize an atmosphere surrounding asubstrate during a production process.

As such there is a present need to provide an alternative dense fluidspray cleaning and separation apparatus and process which overcomes thelimitations of conventional dense fluid spray technology and provides anenvironmentally-safe cleaning and finishing alternatives to organicsolvents.

As such there is a present need to provide clean and effectiveelectrostatic control method during sublimable cleaning processes. Sinceelectrostatic charging is most prevalent in cryogenic cleaning such ascarbon dioxide, argon or liquid nitrogen blasting—a three-dimensionalionization method and device is needed to resolve electrostatic chargingeffects in complex substrates being cleaned, regardless of composition,shape and size.

SUMMARY OF THE INVENTION

There have been many patents issued, and in this decade particularly,for solid-phase cleaning devices and processes. None employ a coaxialmomentum transfer mechanism using thermal-propulsion control of particlevelocity and size described herein. Improved coaxial dense fluid spraycleaning processes and apparatuses have been developed and are describedherein which greatly improve cleaning performance, operationalcharacteristics, adaptability and versatility over U.S. Pat. No.5,725,154 by the present. Most importantly, the present inventionsignificantly improves the performance of conversion of liquid phase C02to solid phase and control of particle size and velocity.

The present invention provides the following new improvements(embodiments):

The present invention changes temperature and pressure of an inertoptionally, ionizable propellant gas over a wide range of temperaturesfrom 70 F to 300 F and pressures from 30 psi to 10,000 psi—this changesthe physicochemical and kinetic characteristics of an enhanced snowparticle mass generated within a condensor tube located at the center ofa coaxial delivery system. Particle size, density, apparent hardness andvelocity of a stream of condensed carbon dioxide can be preciselycontrolled by altering the temperature and pressure of the propellant incombination with altering the length of enhanced condensation tube whichsupercools and condenses precisely injected amounts of liquid carbondioxide. An enhanced solid particle-gas mixture is produced prior tocombining with condensation tube and propellant gas tube assemblieswithin a coaxial delivery line. A device called an EnhancedJoule-Thompson Condensation Reactor (EJTCR), containing a coiled orlooped reaction tube having various lengths and diameters, is used toproduce and densify a mixture of solid carbon dioxide particles(Enhanced Snow) from a source of purified liquid carbon dioxide. TheEJTCR loop is thermally insulated and grounded and is comprised ofvarious lengths and inside diameters of polyetheretherketone (PEEK)tubing. Because most of the condensation and sublimation heat transferoccurs within the EJTCR loop, the result is improved efficiency of theinitial condensation reaction process. A propellant stream comprisingpressurized, heated, inert and optionally ionized gas is produced in aseparate subsystem. Purified inert gases such as carbon dioxide(preferred), nitrogen and clean dry air are heated using an in-lineheater, filtered and ionized using an in-line DC ionizer assembly.

The two streams are first indirectly mixed (ion transfer and heattransfer) using various lengths, diameters and compositions of coaxialcondensation assemblies and then directly mixed (heat transfer andmomentum transfer) using various thrusting and mixing nozzle designs.

The efficiency, in relation to snow mass generated and cleaning energyperformed, of the present invention is increased substantially overconventional Type I snow cleaning designs. Moreover, the presentinvention produces excess heat remaining following transfer, mixing andspraying operations, in accordance with the Carnot equation, whichprovides simultaneous local environmental control through inerting andthermostatting phenomenon.

The present invention describes several new and improved coaxialconfigurations, including interchangeable condenser tube assemblies,co-solvent injection system, various nozzles, manipulator and pistolgrip.

The present invention further teaches a method of adding liquid and gasphase additives an enhanced condensation tube which are mixed anddispersed within the dense solid phase prior to injection and mixingwithin a nozzle. This provides improved physicochemical characteristicsof the resulting spray cleaning agent such as improved contaminantsolvency and lower tribocharging upon contact with a substrate.

The present invention provides a process and apparatus which destroyselectrostatic charges generated through tribocharging via direct contactof solid carbon dioxide particles to the substrate as well as cool andheated gas movement over adjacent surfaces. Unlike prior art approachesto this problem using gas delivered or radioactive sources of chargedcounter-ions, the present invention applies soft x-ray radiation(photons) to the stream of snow particles and substrate simultaneously.The present invention is superior over prior art in that electrostaticcharges are destroyed in transit, during contact at the solid-solidinterface and during sublimation at the surface.

The present invention teaches an improved cleaning and production toolcombining a semiconductor laser operating at the near-infrared region.Using such as laser simultaneously with the present invention providesthe following unique process capabilities:

-   -   1. Thermal drying of substrates before, during and following        snow cleaning.    -   2. Superior spot heating during snow cleaning to assist with        contaminant separation (lower stiction).    -   3. Post snow cleaning production adjunct operations such as a        laser welding, thermal curing, and soldering.

This embodiment uses a low-cost diode laser operating in the nearinfrared at a wavelength of between 780 and 940 nm.

Another feature of the present invention is the combination of arelatively new analytical technique called Optically Stimulated ElectronEmission (OSEE) spectroscopy, also called photoelectron emission (PEE),with the present snow cleaning processes and apparatus. OSEE providesfor instantaneous feedback to a host computer controlling and applyingthe cleaning process. Real-time correlation between cleaning parameterstemperature, pressure, condensation tube length and contact time) andOSEE cleanliness can be established in-situ and used to verify surfacecleanliness following each cleaning operation.

Another aspect the present invention is the addition of solid abrasivesto the propellant gas supply. Mixing solid abrasives with the dense snowmass provides an improved microabrasive finishing ofsubstrates—cryogenic microabrasive finishing. The snow spray embrittlessurface features such as burrs during simultaneous impingement ofabrasive snow additives. The surface features of the substrate becomeharder at a lower temperature than the subsurface—therefore surfacefinishing is aided through an increase in hardness (less rolling androunding of edges and burrs). Following this the spray is used to removeresidue dusts and residues from the finished substrate.

Finally, the present invention discloses a cleaning system and systemsoftware for utilizing the various examples described above in a closedworkcell using a centralized multi-axis programmable robot operating ina circular workcell pattern and using various stations having increasingparticle cleanliness. This embodiment teaches the use of various robothand tools—pick and place tool in combination with a cleaning tool,cleaning-laser tool, cleaning-inspection tool, or cleaning-ionizationtool. Substrates are first picked up using a pick and place tool andmoved from a dirty loading zone into a cleaner process zone. The robotthen changes hand tools, placing the hand tool in a cleaning fixture forsubsequent cleaning, and picks up any one of several novel snow orsnow-process robots tools. Following robotic cleaning and/or processing,the robot cleans the pick and place tools critical surfaces, andreplaces the cleaning tool with the newly cleaned pick and place tool.The cleaned substrate is picked up and placed in a still cleaner unloadzone. The combination of a zoned workcell with a programmable robot,software and novel cleaning and cleaning-production tools provides aneconomical, versatile and adaptable cleaning and production tool.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention will beobvious to those of ordinary skill in the art after having read thefollowing detailed description of the preferred embodiments which areillustrated in the various figures summarized below.

FIG. 1 a is a block diagram illustrating a dense fluid spray cleaningapparatus including an EJTCR loop in accordance with the invention.

FIG. 1 b is a graph illustrating the relationship between particle sizeof solid carbon dioxide and propellant gas temperature with a constantsupersonic thrusting pressure.

FIG. 1 c is a graph illustrating the relationship between velocity ofsolid carbon dioxide particles and propellant gas temperature with aconstant supersonic thrusting pressure

FIG. 1 d is a graph illustrating the relationship between solid carbondioxide particle relative hardness and length of condensation tube witha constant diameter.

FIG. 1 e is a graph illustrating the relationship between velocity ofcondensed solid carbon dioxide-subcooled gas mixture and length ofcondensation tube with a constant diameter.

FIG. 1 f is a diagram illustrating the difference between conversion ofheat to work (velocity) produced by conventional devices and a device inaccordance with the present invention.

FIG. 1 g is a graph comparing the difference between substratethermostatting and local ambient inerting phenomenon in conventionaldevices and a device in accordance with the present invention.

FIG. 1 h is a diagram illustrating the cumulative effect produced by thepresent invention with respect to local environmental control ofsublimation heat management, ambient inerting and tribocharge control.

FIG. 1I is a diagram illustrating the effect upon local ambientatmosphere and substrate using conventional snow cleaning.

FIG. 1 j is a graphical representation of the effect upon local ambientatmosphere and substrate using conventional snow cleaning with a sheathof inerting gas.

FIG. 1 k is a graphical representation of the effect upon local ambientatmosphere and substrate using the present invention.

FIG. 1 l is a phase diagram showing effect on relative snow density andgeneration efficiency with respect to EJTCR loop length and diameter.

FIG. 2 a is a schematic drawing of a dense fluid spray cleaningapparatus including an EJTCR loop in accordance with the invention.

FIG. 2 b is a block diagram illustrating various embodiments of thepresent invention.

FIG. 3 is a cross-sectional view of a spray applicator for use inaccordance with the present invention.

FIG. 4 is a cross-sectional view of a hypersonic spray applicator foruse in accordance with the present invention.

FIG. 5 is a cross-sectional view of an additive spray applicator for usein accordance with the present invention.

FIG. 6 is a cross-sectional and a front view of a conductive sprayapplicator for use in accordance with the present invention.

FIG. 7 is a cross-sectional and a front view of a fanned sprayapplicator for use in accordance with the present invention.

FIG. 8 is a schematic drawing of a multiple spray applicator assemblyfor use in accordance with the present invention.

FIG. 9 is a partial cross-sectional view of a extension manipulator foruse in accordance with a spray applicator.

FIG. 10 is a partial cross-sectional view of a handgun spray applicatorfor use in accordance with the present invention.

FIG. 11 is a schematic drawing illustrating a photoelectron generatorintegrated with an spray applicator for use in accordance with thepresent invention.

FIG. 12 is a schematic drawing illustrating a diode laser integratedwith an exemplary spray applicator.

FIG. 13 is a schematic drawing illustrating both photoionization anddiode laser heating.

FIG. 14 is a top and side schematic drawing illustrating anenvironmentally controlled robotic cleaning and inspection workstationfor use in accordance with the present invention

FIG. 15 is a schematic drawing illustrating architecture forautomatically controlling a robotic substrate cleaning process,inspection process and associated environment using a computer/PLC andsoftware.

FIG. 16 is a schematic drawing illustrating a cryogenic microabrasivesurface finishing apparatus and process in accordance with theinvention.

FIG. 17 is a schematic drawing illustrating use of dynamic pressurecontrol during a substrate cleaning operation

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention describes an improved adjunct separation mechanism whichinvolves the formation of variable-geometry microscopic substancescalled “Snow Gels” comprised of trace organic surface residues (treatedas solvents or solutes) dispersed in solid phase carbon dioxideparticles (treated as a subcooled solvent-solute matrix). This mechanismis supported by solubility research performed by Myers and Prausnitz (M.N. Myers and J. M. Prausnitz, “Thermodynamics of Solid Carbon DioxideSolubility in Liquid Solvents”, Ind. Eng. Chem. Fund., 4, 209,1965) inwhich they treat solid carbon dioxide (solid-state xenon has also beenstudied) as a subcooled liquid to determine cohesive energy values.

Solid carbon dioxide possesses electron acceptor (Lewis Acid) andmolecular quadrapole moment properties which contribute to ahydrocarbon-like cohesion energy and complex forming ability withhydrocarbons. Solid carbon dioxide has a measured solubility parameterof between 23 MPa^(1/2) and 20 MPa^(1/2) in the temperature range of 140K to 200 K that is comparable to its liquid-state cohesive energy.Therefore, the removal of thin films of hydrocarbons using solid-statecarbon dioxide may occur through a liquid-subcooled liquid/particle masstransfer mechanism, whereas the Snow-Hydrocarbon interface is proposedto be the continuous formation and removal of a lyophilic crystallinegel or rigid colloid which I call a snow-gel. This mechanism is furthersupported by the fact that heavy metals are insoluble in liquid carbondioxide, but should form complexes or colloids with organic-like solidslike solid-phase carbon dioxide. Cleaning tests show a reduction inmetal ion contamination using solid phase cleaning.

The proposed compression-liquefaction mechanism may be an intermediatestep of snow-gel formation, whereby the liquid-hydrocarbon istransformed instantaneously into a snow-gel particle through rapidevaporation and cooling. Research by Myers and Prausnitz confirms thesolubility of solid carbon dioxide with several hydrocarbon systems.Laboratory experiments confirm the formation of a stable gel-likesubstances with various mixtures of hydrocarbon liquids and solid carbond a schematic diagram illustrating a dense fluid spray cleaningapparatus including an enhanced joule-thompson condensation reactor(“EJTCR”) loop in accordance with the invention ioxide.

Referring to FIG. 1 a., there is shown a block diagram illustrating adense fluid spray cleaning apparatus in accordance with the invention.The apparatus includes an (EJTCR) (2), a CO₂ supply (3), a spray nozzle,a thermal inert or thermal ionized gas (propellant) generator (4), apremix chamber (6), and a mixing chamber (8).

Small amounts of liquid carbon dioxide, preferably from about 5 to about200 lbs/hr, more preferably from about 10 to about 30 lbs/hr, is meteredfrom the CO₂ supply (3) under a pressure of between 300 and 1000 psi andat a temperature of between 0 F and 85 F and injected through a spraynozzle into the EJTCR loop. The liquid carbon dioxide expands rapidlyinto a mixture of approximately 50% solid and 50% subcooled gasimmediately upon injection. Following this expansion, the resulting50:50 solid:gas mixture is introduced into a thrust forming cavityhaving various geometries to produce a supersonic spray stream.

The EJTCR (2) comprises a coiled section of polyetheretherketone (PEEK)tubing (loop) which is overwrapped with a grounded conductive shielding(Faraday Cage) such as a metal spring or metal foil and furtheroverwrapped with a thermally insulative material such as polyolefin.PEEK is a preferred loop material because it is highly flexible, canwithstand very high pressure and very low temperatures, and is a goodthermal insulator.

In the present invention, the initial expansion is a “seeding” process.As the seed or slug of subcooled liquid and gas mixture travels down thelength of the EJTCR loop, the gas is condensed or coagulated into solidand solid is compacted into a dense mass. The EJTCR loop has an O.D. offrom about 1/32″ to about ⅛″, preferably about 1/16″ and an ID of fromabout 0.0025″ to about 0.080″, preferably from about 0.02 to about0.08″. The EJTCR loop diameter creates expansion of the gas which causesa temperature decrease. The EJTCR loop has a length of from about 6″ toabout 20 ft, preferably from about 4 ft to about 5 ft. The EJTCR looplength creates compression through drag forces. The temperature decrease(decreasing with increased loop length) is observed as a result of heattransfer from expanding gas molecules—this results in a condensation ofexpanding gas into solid phase (kinetic energy is converted intopotential energy). As the mixture travels the length of the thermallyinsulated EJTCR loop, very efficient heat transfer occurs. As such, thelonger the EJTCR loop—the more efficient the coagulation process.Moreover, increasing the length of the EJTCR loop increases pressure anddrag within the loop—causing the solid particles to pack together into adense solid carbon dioxide mass.

Microdroplets of liquid carbon dioxide are caused to shear underturbulent conditions (Reynolds Number>10,000) within the EJTCR loop.Gas-particle velocity decreases and turbulent shear increases over thedistance of the loop. The longer the loop—the higher the turbulentshear. This increase in shear increases coagulation of liquid and gasphases into solid phase by contacting vapor within the loop with newlyformed solid particles having a temperature that is below the saturationtemperature. Heat transfer within the loop is a combination of twomodes—conduction and convection. The enhanced condensation processinvolves mass transfer simultaneous with heat transfer. The EJTCR loopmaintains high pressure and low temperature over along distance (time).Increasing pressure, decreasing temperature and increasing time enhancethe condensation process. The net result of the EJTCR process is anefficient and controllable conversion of liquid carbon dioxide into arelatively slow moving dense solid mass of carbon dioxideparticles—called enhanced snow. Increasing the loop length for a givenloop internal tube diameter increases conversion. The purpose ofwrapping the loop with grounded electrical shielding is to drain awayelectrostatic charges generated during the coagulation process andmovement of this dielectric mixture through the EJTCR loop. Anadditional overwrap of thermal insulation on the loop prohibits heattransfer from the ambient atmosphere which would be detrimental toparticle growth.

A thermal inert or thermal inert ionized propellant gas generator (4)provides a source of propellant gas. Suitable propellant gases includecarbon dioxide, nitrogen or clean dry air or other gases which can bepurified, filtered, heated and optionally ionized. The preferredpropellant gas is carbon dioxide. The propellant gas is used herein notonly as a propellant, but simultaneously as a solid particle sizemodifier, ion neutralizer, inerting agent, and thermostat agent. In someembodiments the gas generator includes an in-line ionizer for ionizingthe propellant gas to produce positive and negatively charged gasmolecules. This mixture of charged gas molecules is used to bathe thesnow tube and propellant gas tube assemblies within premixchamber—neutralizing charges created by the movement of dielectric gasand solids within each tube. An alternative design uses a grounded metalcage to drain away charges generated. A benefit of using the in-lineionizer is that the present invention can be used to spray thermalionized gas on a substrate following cleaning to insure that no residualelectrostatic charges are left behind following cleaning which mightattract airborne particles.

The premix chamber (6) is a section where the propellant gas isindirectly contacted with the enhanced snow from the EJTCR. Thepropellant gas is caused to flow over a predetermined length of flexible(PEEK) or rigid (stainless steel) inner tube, the snow tube, carryingthe enhanced snow. The propellant gas is carried in an outer coaxialtube, the propellant gas tube, which itself is either flexible (Teflon)or rigid (stainless steel. The coaxial premix chamber transfers heat,and optionally ions, under controlled conditions from the propellant gasto the enhanced snow. Changing the type of premix snow tube from PEEK tostainless increases heat conduction. Heat contained in the propellantgas slowly diffuses through the snow tube and is transferred to theenhanced snow. This causes the enhanced snow to sublimate. Increasingthe heat content of the propellant gas and increasing the contact time(length of premix chamber) increases the sublimation. As such, theenhanced snow is expanded and accelerated towards the end of the snowtube. It has been discovered that heating the snow tube greatly improvessnow particle flow from the EJTCR and up to the mixing chamber. Withoutwishing to be bound by a theory of operation, it is believed that a thinlaminar high velocity carbon dioxide gas sheath is produced between thesnow particles and the inner wall of the PEEK or stainless tube wall.This is analogous to lubrication and prevents the dense snow particlesfrom packing, clogging and spitting from the snow tube. There is asignificant difference in snow tube flow characteristics with andwithout the presence of propellant gas flow. Moreover, heat transferthrough the snow tube initiates the process of solid particle sizereduction and provides an initial impulse to the mixture prior toinjection into the mixing chamber.

The propellant gas and enhanced snow are combined in the mixing chamber(8) to produce a composite supersonic spray stream. The mixing chamberincludes a nozzle wherein the inner snow tube is fed into a mixingsection of a convergent-divergent mixing nozzle. The propellant gas iscompressed through the convergent section that increases pressure andreduces velocity, mixed with the enhanced snow particles and expandedthrough a divergent section wherein the pressure of the mixture isreduced which causes the mixture to rapidly accelerate out of the mixingchamber. The heat content of the propellant gas generates a significantimpulse from sublimating the dense enhanced snow mass. Depending uponthe nature of the mixing nozzle, different impulse and spraying patternscan be produced. Depending upon the temperature and pressure of thepropellant gas, a variety of particle size ranges can be produced andthe resultant mixture(10), has a much higher energy content than thoseproduced using conventional snow spraying devices.

Having discussed in general the basic operation and characteristics ofthe present invention, following is a detailed discussion of each corecomponent and adjunct systems and processes that control and optimizethe present invention.

1 b illustrates the relationship between particle size of solid carbondioxide and propellant gas temperature with a constant supersonicthrusting pressure. By varying the temperature of a propellant gas and(1) first indirectly contacting propellant gas with the enhanced snowthrough a thin heat transfer wall (Premixing heat and ions) and then (2)directly mixing the propellant gas with the enhanced snow particlemass—the average solid carbon dioxide particle size of the resultingspray stream can be altered considerably. The particle size can bevaried over a wide range from 100 micrometers (12) to 0.2 micrometers(14) by varying the temperature of the propellant gas from 70 F to 300F. This variance is relatively constant for a fixed propellant pressure,fixed EJTCR loop length and inner diameter and premix distance.

FIG. 1 c illustrates the relationship between velocity of solid carbondioxide particles and propellant gas temperature with a constantsupersonic thrusting pressure. By varying the temperature of apropellant gas and (1) first indirectly contacting propellant gas withthe enhanced snow through a thin heat transfer wall (Premixing heat andions) and then (2) directly mixing the propellant gas with the enhancedsnow particle mass—the average solid carbon dioxide particle velocity ofthe resulting spray stream can be altered considerably. The particlevelocity can be varied over a wide range from less than 500 ft/sec (16)to greater than 1600 ft./sec (18) by varying the temperature of thepropellant gas from 70 F to 300 F. This variance is relatively constantfor a fixed propellant pressure, fixed EJTCR loop length and innerdiameter and premix distance.

FIG. 1 d is a graph illustrating the relationship between solid carbondioxide particle relative hardness and length of condensation tube witha constant diameter. By varying the length of the EJTCR loop—therelative density (d=p/97.6) of the solid carbon dioxide particles streamcontained within the snow tube can be altered considerably. The relativedensity can be varied over a wide range from 0.5 g/cm3 (20) toapproaching 1 g/cm3 (22) by varying the length of the EJTCR loop from0.1 meters to 10 meters. This variance is relatively constant for afixed diameter of thermally insulated PEEK condensation tube.

FIG. 1 e is a graph illustrating the relationship between velocity ofcondensed solid carbon dioxide-subcooled gas mixture and length ofcondensation tube with a constant diameter. By varying the length of theEJTCR loop—the velocity of the enhanced solid carbon dioxide particlesstream contained within the snow tube can be altered considerably. Thevelocity is varied over a wide range from 600 ft/sec (24) to approaching50 ft/sec (26) by varying the length of the EJTCR loop from 0.1 metersto 10 meters. This variance is relatively constant for a fixed diameterof thermally insulated PEEK condensation tube.

FIG. 1 f is a diagram illustrating the difference between conversion ofheat to work (velocity) produced by conventional devices and a device inaccordance with the present invention. By varying the temperatures ofmixing of the propellant gas having variable pressure and hightemperature with an enhanced snow particle stream having high densityand low temperature, and where the propellant gas velocity is supersonicand the enhanced snow stream velocity is subsonic—the Carnot Efficiency(E—work performed), expressed as E=Tmax−Tmin/Tmax, can be altered over arange of efficiencies and results in a much improved E over conventionalsnow spray streams. The E can be varied over a wide range from 30% (28)to greater than 50% (30) by varying the temperature of the propellantgas from 70 F to 300 F. This variance is relatively constant for a fixeddiameter of thermally insulated PEEK condensation tube, premix chamberand propellant gas pressure. By contrast, conventional snow streams havea calculated E of between 5% (32) and 30% (28). The work performed inthe present invention is expressed as impulse, thrust or propulsion(34). The residual heat of the propellant gas, expressed as heat notconverted into work (1-CE), is used in the present invention for in-situambient inerting and thermostatting at or near the substrate duringimpact of supersonic snow particles (36).

By contrast, conventional snow sprays produce a 50:50 mixture of verycold solid and gas. The gas in this conventional approach is also thesolid propulsion agent—however its temperature is near the saturationtemperature. As a result, this gas produces undesirable environmentaleffects such as ambient inclusion and condensation of moisture and rapidfreezing of the substrate.

FIG. 1 g is a graph comparing the difference between substratethermostatting and local ambient inerting phenomenon in conventionaldevices and a device in accordance with the present invention. Theresultant temperature of a composite spray used in the present inventionis much higher and is variable as compared to conventional snow spraystreams. To demonstrate the thermostatting characteristics of thepresent invention, a measurement of average surface temperature duringnormal scan spraying (1 inch/sec) a 4 inch by 4 inch (16 in2) aluminumplate using a conventional snow gun (Va-Trans-SnoGun) and the presentinvention shows the various thermal profiles produced over time. Aconventional snow spray gun produces an average surface temperature of−20 F after 10 seconds of scan spray (38) and almost instantaneouslymoisture is condensed on the substrate. By contrast spraying using thepresent invention produces a different thermal profile for eachsuccessive increase in temperature−150 F (40), 200 F (42) and 250 F(44). Although the sprayed surface temperature of the substrate droppedbelow the ambient dew point (46)—there was no visible condensation onthe substrate. This is due to the local inerting characteristics andphenomenon associated with the present invention.

FIG. 1 h is a diagram illustrating the cumulative effect produced by thepresent invention with respect to local environmental control ofsublimation heat management, ambient inerting and tribocharge control.The propellant gas used in the present invention is used uniquely as adynamic particle size control agent, ion transfer agent, propulsionagent, thermostatting and inerting agent. By controlling propellant gastemperature, flowrate and pressure, the local environment above and onthe surface being cleaned is controlled. Environmental controlcharacteristics include simultaneously supplying heat to sublimatingsolid particles upon impact (sublimation heat energy—thermostatting) andexcluding the ambient atmosphere from the area being cleaned (inerting).

Referring to FIGS. 1 i, 1 j and 1 k, the environmental control benefitsprovided by the present invention are illustrated by comparingconventional snow cleaning methods and devices to the present invention.FIG. 1 i shows the environmental dynamics of a simple conventional snowspray device. An extremely cold stream of solid and gaseous carbondioxide (48) is directed at a substrate (50). Two undesireablephenomenons occur simultaneously. First, the ambient atmosphere (52)which surrounds the spray stream (48) and which contains particle,moisture and hydrocarbon contamination is condensed into the cold spraystream (48). Once incorporated into the stream, the contaminants areimmediately deposited onto the substrate (50). A second undesirableeffect is heat transfer from the substrate. Because the conventionalsnow stream is very cold, upon impact the cleaning spray sublimates andextracts significant heat (54) from the surface. The surface must beheated continuously from below or above to compensate for thissublimation heat energy.

FIG. 1 j shows the environmental dynamics of a simple conventional snowspray device with a shroud of heating gas (called sheath flow). Anextremely cold stream of solid and gaseous carbon dioxide (56) isdirected at a substrate (58) with a sheath flow of inert gas flowingconcentrically about the snow stream (60). In this application, ambientatmosphere (62) is excluded from the center of the cleaning zone. Theundesirable effect here is the same as a simple conventional snow sprayoperation—heat is transferred from the substrate. Because the centerstream is a conventional snow stream and is very cold, upon impact thecleaning spray sublimates and extracts significant heat (64) from thesurface. The surface must be heated continuously from below or above tocompensate for this sublimation heat energy or the sheath flow mustremain on for some period of time following the snow cleaningspray—operating in a pulse mode.

FIG. 1 k shows the environmental dynamics of the present invention. Anextremely cold stream of solid and gaseous carbon dioxide is mixed withsuperheated gas to produce the stream (66) which is directed at asubstrate (70). In the present invention, ambient atmosphere (72) isexcluded from the center of the cleaning zone and, unlike conventionalapproaches, heat (74) is transferred to the surface of the substrate.Because stream contains residual heat, it is expanding from the centralcleaning zone and excludes the ambient environment. Additionally, whenthe entrained snow particles sublimate at the surface, heat (74) isextracted preferentially from the surrounding component around, aboveand at the surface of the substrate. The present invention packagessublimation heat and delivers it with the solid snow particle. Theresult is that the surface does not have to be heated continuously frombelow or above using external heat sources to compensate for thissublimation heat energy and separate inerting atmospheres do not have tobe incorporated.

FIG. 1 l shows the overall relationship between the EJTCR loop lengthand internal pressure with respect to the generation of a dense mass ofsolid carbon dioxide in relationship to pressure and temperatureconditions on the carbon dioxide phase diagram. Referring to the figure,during expansion from gas-saturated liquid phase (A) a conventional snowcleaning nozzle produces a cleaning mixture (B) comprising a maximum of50% solids and 50% cold vapor. Conventional snow spray cleaning mixturestend to be very porous following expansion because the microscopic sizedsolid particles rapidly sublimate upon exposure to ambient conditions oftemperature and pressure. Conventional snow sprays are controlledthrough the use of convergent-divergent nozzle designs

By contrast, in accordance with the inventive device, a small quantityof gas saturated liquid is injected into a long thermally isolated andelectrically grounded loop (called the EJTCR Loop herein) to produce acontrolled dense mass of predominantly solid carbon dioxide (C). TheEJTCR snow (called enhanced snow herein) generation process is directlycontrolled through loop length and diameter. For a fixed internaldiameter of between 0.007 inches and 0.080 inches and varying the lengthof the loop from 0.1 to 10 meters (expansion volume from 5 ul to 30milliliters), various relative densities of snow mass as described abovecan be produced. In general, for a fixed internal diameter and byelongating the expansion loop—variable densities can be produced. Asshown in the Fig., long EJTCR loops result in a lower internal looptemperature and higher internal loop pressure—both favor solidsgeneration.

The following is a more detailed description of an exemplary apparatusfor performing the present invention based upon the above corestructure.

Referring to FIG. 2 a, a supply of carbon dioxide gas (76) is connectedto a tee (78) which splits the gas stream into two high pressure gaseousstreams. The carbon dioxide gas supply is derived from a supply of gassaturated liquid (80) held under a pressure of between 300 psi and 1000psi and a temperature of between 0 F and 85 F. A pipe (82) feeds onefraction of the high pressure gas to a regulator (84) which iscontrolled using a pressure controller (86) and pressure sensor (88).Regulated carbon dioxide gas feeds from the regulator (84) via a feedline (90) into a valve (92). The valve (92) is connected via a feed line(94) which feeds pressure regulated carbon dioxide gas into a heaterassembly (96). The heater assembly (96) comprises a temperaturecontroller (98) and temperature sensor (100). The heater assembly (96)heats the pressure regulated carbon dioxide gas which feeds pressureregulated and heated carbon dioxide gas via feed line (102) into aparticle filter assembly (104). The pressure regulated, heated andfiltered carbon dioxide gas is fed via feed line (105) into an optionalionizer assembly (106) to create thermal ionized or thermal inert carbondioxide gas. The optional ionizer assembly (106) comprises a tee. (notshown) containing an electrode (not shown) which is connected to powersupply (108) which generates both positive and negative potential on theelectrode. Pressure regulated, heated, filtered and optionally ionizedcarbon dioxide gas is fed via feed line (110) into a coaxial premixchamber (112).

A second fraction of unregulated high pressure carbon dioxide gas is fedvia feed line (114) into catalytic purifier (116), available fromM.O.S.T, Wisconsin. The unregulated high pressure and catalytic purifiedgas is fed via feed line (118) into a condenser unit (120) whereupon itis condensed, via heat transfer or pressure pump, from a gas phase intoa liquid phase. In an alternative embodiment, not shown, the purifiedgas exiting the catalytic purifier (120) is further split into twostreams—providing an ultrapure propellant gas supply for practicing thepresent invention. The purified liquid carbon dioxide is collectedthrough condensing line (122) into a stainless steel reservoir (124).Purified liquid carbon dioxide is transferred via feed line (126) to amicrometering valve (128), which controls the feedrate through valve(130). Liquid carbon dioxide is fed from valve (130) via feed line (132)and through an in-line particle filter (134) into an enhancedjoule-thompson condensation reactor (EJTCR) loop (136). The EJTCR loopmay be constructed of various lengths and internal diameters of coiledPEEK tubing, which are coiled, wrapped in electrically conductive andgrounded (138) shielding (not shown) and overwrapped in a suitablethermal insulation such as polyolefin shrink tubing (not shown). The endof the EJTCR loop is fed into and down the center of premix chamber(112) serving as a flexible inner snow tube (142) up to the mixingchamber (144). Optionally, the end of the EJTCR loop may be integratedto the beginning of the premix chamber (112) using a suitable connector(140) to change the PEEK connection into a rigid polished stainlesssteel snow tube (142).

The premix chamber (112) comprises an outer flexible or rigid propellantgas line (146) housing a centrally located flexible or rigid snow tube(142). The snow tube (142) may be wrapped in a grounded metallicshielding (not shown) to dissipate electrostatic charges from solidcarbon dioxide flowing within the snow tube (142) and propellant gasflowing within the propellant gas tube (146). Alternatively, thepropellant gas tube (146) may be wrapped in a grounded metallicshielding to provide beneficial electrostatic charge control. Thepropellant gas tube (146) is connected to the mixing chamber (144)wherein the snow tube (142) is inserted into the center of the mixingchamber (144).

The mixing chamber (144) comprises a convergent-divergent nozzleconfiguration wherein the snow tube (142) may be positioned to be withinany position from the divergent section (148), the mixing section (150),or the divergent section (152) of the mixing chamber (144). Positioningthe snow before the convergent section or after the divergent sectioncauses the stream to be highly turbulent and unpatterned. The preferredposition for the snow tube is within the mixing section (150) whereinstructural changes can be made to both the convergent and divergentsections to optimize the pattern and thrusting of the. An example of adynamically adjustable nozzle configuration is given in U.S. Pat. No.,154, which patent is herein incorporated by reference.

Two basic sensors are used to determine if 1) carbon dioxide supplyproblems exist and 2) purification system problems exist. A pressuresensor (152) located on the carbon dioxide gas supply line (154) andfeeding the tee (78) is used to determine if the gaseous supply isdepleted. An optical liquid level sensor (156) connected to the purifiedliquid carbon dioxide reservoir (124) determines if liquid is beingcondensed within the condenser unit (120).

Some embodiments additional include an injection system forincorporating additives. For example additives can be included into theliquid carbon dioxide stream. A purified liquid carbon dioxide additiveinjection system includes a source of additive (158) connected to thepurified liquid carbon dioxide reservoir via an injection pump (160).

In other embodiments, an additive injection system (162) is integratedfollowing the EJTCR loop using a tee (164). Suitable additives at thisconnection point also include alcohols, surfactants, gases, and thelike. In still other embodiments, an additive injection system (166) isintegrated into the mixing chamber (144) using a tee (168). Finally, anadditive injection system (170) may be integrated into the propellantgas tube (146) using a suitable connection tee (172). Suitable additivesat this connection point include alcohols, surfactants, gases, and thelike.

Basic control systems for the present invention are also illustrated inFIG. 2 a. Propellant gas pressure may be dynamically changed over timeusing a digital or analog input (174) to the pressure controller (86).Propellant gas temperature may be changed over time using a digital oranalog input (176) into the propellant gas temperature controller (98).Similarly, the manual micrometering valve (128) may be replaced with adome-loaded digital metering valve. An electronic switch (178) isprovided to turn the optional propellant gas ionizer on and off. Anelectronic switch (180) is provided to turn on the flow of regulatedcarbon dioxide into the heater assembly (96). An electronic switch (182)is provided to turn on and off the injection of metered purified liquidcarbon dioxide into the EJTCR loop (136) through the filter assembly(134). Finally, an electronic switch (184) is provided to the additiveinjection pump (160).

An additional embodiment of the present invention includes a method forpreventing and eliminating electrostatic charges generated duringcontact of snow, with the substrate. Shown in FIG. 2 a is a photoionizer(186) which is electronically turned on and off using an electronicswitch (188). This embodiment directs photoelectrons at the cleaningtarget area, bathing the spray and substrate with ionizingphotoelectrons. The photoelectrons ionize multiple interphases—gas-gas,solid-gas and solid-solid, destroying unbalanced electric chargesin-situ and during creation.

Another embodiment of the present invention includes a diode laser (190)which is turned on and off using an electronic switch (192) and powercontrolled using a digitally controlled power supply (not shown). Thediode laser provides coherent heating radiation to a spot (cleaningtarget) which is used in the present invention to enhance cleaning andserves as a combination of cleaning, welding, thermal curing anddrilling tools.

Still another embodiment of the present invention includes a surfaceanalysis device, such as an ultraviolet photoemission analyzer, toprovide in-situ feed-back and control of the cleaning process. Anultraviolet radiation optically stimulated electron emission sensorprovides surface cleanliness data which can be dynamically correlated tothe various control parameters—pressure, temperature, snow injectionrate and time. This capability provides an in-situ means of calibratingand validating the cleaning process. As shown in FIG. 2 a, an OSEEsensor (194) is coupled to an on/off switch (196) and integrated with aspectroscopic analyzer (not shown) which provides feedback throughsoftware to the process control software.

FIG. 2 b is a block diagram illustrating various embodiments of thepresent invention. This figure shows the EJTCR (198), the ThermalInert/Ionized Gas Propellant Generator (200), the Premix Chamber (202)and the Mixing Chamber (204), along with a Photoionization System (206),a Diode Laser System (208), an Optically Stimulated Electron EmissionAnalyzer (210), a Multi-axis programmable robot system (212), a roboticenvironmental control system (214) and computer software (216).

FIG. 3 shows an economical mixing applicator comprising three integratedcomponents. The first component comprises a nozzle (218) having a rearthreaded male section with a propellant tube sleeve (220) and a frontconvergent-divergent mixing nozzle (222). The second component is apropellant tube connection sleeve (224) having a threaded femaleconnection and an elongated and tapered inner sleeve (228). The thirdcomponent is the premix chamber comprising a flexible or rigidpropellant tube (230) and a flexible or rigid Snow Tube (232). Assemblyof the three components is shown in the figure and described as follows:The propellant tube (230) is pushed over the propellant tube sleeve onthe mixing nozzle and located rear of the threaded section (220). Theconnection sleeve (224) is slid over the propellant gas tube andthreaded to the mating male threaded section (220) of the mixing nozzle.This action causes the connection sleeve inner tapered wall (228) tocompress over and grip the outside of the propellant gas tube. The SnowTube (232) is slid into the center of the coaxial assembly andpositioned within the mixing section (234) of the mixing nozzle (218).Once positioned within the mixing nozzle, the Snow Tube (232) iscompressed using a suitable fitting at the entrance of the PremixChamber (FIG. 2 a, 140) to maintain its position.

FIG. 4 illustrates a hypersonic spray applicator for use with thepresent invention. This nozzle is designed for use with propellant gaspressures of between 100 psi to 5000 psi or more to produce thehypersonic spray. It is constructed of stainless steel and contains atee section (236) wherein the PEEK Snow Tube (238), comprising the endof the EJTCR loop, is brought into and sealed to the tee section andmated to a section of stainless steel Snow Tube (240) using a pair ofbulkhead compression fittings (242). High pressure propellant gas is fedinto the tee (244) from the propellant gas generator (not shown). Thebody of the hypersonic spray applicator is grounded (246).

FIG. 5. illustrates an additive injection apparatus for use with thepresent invention. The propellant gas nozzle contains a small bore (248)extending through and into the entrance of the mixing section (250), ata 45 degree angled bore, through which a small PEEK or stainless steelinjection needle (252) is inserted. During spraying operations, smallamounts of liquids or gases are fed through the needle (252) into themixing chamber.

FIG. 6. illustrates a conductive brush cleaning apparatus for use withthe present invention. The nozzle contains conductive nylon bristles(254) concentrically positioned about the exit of an extended lengthmixing section (256). During spray cleaning operations, the brushassembly aids in dislodging large particles and residues whilemaintaining a ground through the spray applicator body (258).

FIG. 7 illustrates a fan spray cleaning apparatus for use with thepresent invention. The nozzle contains elongated and flattened divergentsection (260) through which the stream is sprayed.

FIG. 8. depicts a multiplexed spray assembly. PEEK tees (262) are usedto split the enhanced snow stream fed from the EJTCR loop (264) intofour individual Snow Tubes (266) which are fed into a multiportedmanifold (268) using a bulkhead compression fitting (270). Affixed tothe manifold are four mixing nozzles (272) through which the Snow Tubeis fed into the mixing sections. Propellant gas is fed into the manifoldthrough a common port (274). Any number of spray heads can be developedas long as the feed diameter from the EJTCR loop is sized to provide anadequate feedrate through the individual snow tubes. The multiportedspray applicator is useful for robotic and machine integrationapplications and produces a large cleaning pattern with only a smallamount of movement in any direction (276).

FIG. 9 illustrates spray manipulator assembly for extending the sprayapplicator into hard to reach areas. The device comprises an adjustablemounting head (278), extension or telescoping shaft (280), and handle(282) with actuation trigger switch (284) and optional propellant gas(ionization) trigger switch (286). The manipulator is integrated withthe generator through a flexible coaxial assembly (286).

FIG. 10. Illustrates a spray handgun assembly for manually holding andusing the spray applicator. The assembly comprises a body (288) throughwhich the spray applicator (290) is fed into and clamped. The handgunbody contains a actuation trigger switch (292) and optional propellantgas (ionization) trigger switch (294). The handgun assembly isintegrated with the generator through a flexible coaxial assembly (296).

FIG. 11 illustrates a photoionizer integrated with the applicator. Asshown in the figure, the photoionizer (298) and spray applicator (300)are mounted on a common manifold (302). The manifold (302) contains aphotoionizer pivot (304) and spray applicator pivot (306) for adjustingthe alignment of each device with respect to the contact cleaning pointon the substrate (308). The photon-cleaning manifold is connected to amulti-axis robot (not shown) using a robotic mount (310). Connecting themanifold to a multiaxis robot provides for any number of possibleorientations and angles. The photoionizer is tunable to provide bothspot and broad-spectrum substrate ionization—the robot provides thefocusing control for both the spray applicator and photoionizer. Anotherfeature shown in the figure is a spin processor (312). The spinprocessor holds the substrate under vacuum (314) via a vacuum chuck(316). The substrate is spun at a rotational velocity of between 20 and5000 rpm. The photon-cleaning manifold is scanned from the interior (asshown) to the perimeter of the substrate while the substrate is spinningbelow. Software is used to control the pressure, temperature andphotoionization process sequencing. In some embodiments the propellantgas pressure is decreased while the manifold moves from the interiorregion (lowest centripetal force) to the perimeter (highest centripetalforce). Using this approach, the actual impact force (cleaning energy)of the particle stream is continuously decreased to compensate for theincreasing centripetal force toward the perimeter -providing consistentcleaning energy across the entire substrate. Another feature is theability to defocus the photoionizer to provide entire substrateionization following cleaning and focused ionization during spraying toprovide intense localized ionization. Finally, the photon-process isperformed in a soft x-ray shielding box (318) to protect workers fromexposure. X-Ray shielding can be most materials of suitable photonabsorbing thickness such as 0.250 inch static safe clear acrylic.

The traditional ionization method uses air to deliver ions to anaffected substrate. However this only works as a line-of-sight solutionand the mechanics of cryogenic spray cleaning eliminates mostline-of-sight ionization opportunities. In solid carbon dioxide spraycleaning, five tribocharging interfaces are present:

-   Interface 1: snow particle—snow particle-   Interface 2: snow particle—gas molecules-   Interface 3: substrate surface—snow particle-   Interface 4: substrate surface—gas molecules-   Interface 5: gas molecules—gas molecules

Moreover, these tribocharging interfaces are three-dimensional andcomprise various phases of matter—solids, liquids (condensed vapors andcontaminants) and gases. Conventional ionization techniques manage oneof two of the interfaces at best and do not manage all dimensions andphases present. For example in air ionization—the contacted surface isaffected only and requires time to deliver the ions in sufficientconcentration to neutralize electrostatic charges. In this example, theatmosphere above and down to the substrate is only affected. The snowstream, snow stream-substrate and backside interfaces of the substrateare not affected by air ionization. Grounding of non-conductors does notwork.

Furthermore, as noted above, the cleaning of non-conductors with solidcarbon dioxide produces many undesirable electrostaticeffects—non-conducting substrates being cleaned charge unevenly withpockets of positive and negative charge, the solid carbon dioxide-gasparticle mix is significantly charged prior to delivery to thesubstrate, the ensuing vapor cloud is highly charged. This also includesconductors which are ungrounded. All of these electrostatic events areoccurring simultaneously during solid carbon dioxide spray cleaningoperations. To date, the traditional techniques have been implemented,with the above-mentioned negative consequences. These problems areovercome by the inventive embodiments which provide a method and devicefor cleaning ESD/EOS sensitive electronic devices with sublimablecleaning agents, and more specifically solid carbon dioxide, withoutproducing undesirable ESD.

Benefits of Combining Photons and Solid Carbon Dioxide:

Heretofore, photoionization has not been implemented in snow cleaning.This may be due to its cost and potential safety issues associated withsoft x-ray radiation. Regardless, this has resulted in those skilled inthe art not investigating the benefits of using x-rays in combinationwith solid-phase carbon dioxide during cleaning or cooling applications.This researcher has investigated the photoelectric-carbon dioxidecombination and reports the following and previously undiscoveredbenefits of this unique combination:

-   -   1) Photoelectrons pass directly into and through the cryogenic        solid spray matrix-creating ions in-situ through ionization of        the gaseous carbon dioxide gas surrounding solid carbon dioxide        particles. This effectively eliminates charge build-up during        transport from the nozzle to the substrate.    -   2) Photoelectrons pass through substrate creating ions on the        front surface (surface being cleaned) and back surface (surface        not being cleaned). This prevents contaminants from passing        around the substrate and sticking to the backside (a.k.a.        electrostatic flypaper effect) during cleaning.    -   3) Photoelectrons pass through the atmosphere between the        cleaning applicator and substrate and behind the substrate        creating a virtual pool of ions within the carbon dioxide        atmosphere, substrate and snow simultaneously. This eliminates        charge build-up within the atmosphere contacting the substrate.    -   4) Unlike air ionization, the photoelectric ionization effect is        enhanced by the motion of gas molecules within the photon beam.        This is very beneficial since the solid carbon dioxide spray        technique produces a very turbulent atmosphere.    -   5) The photoionization effect is 3-dimensional and is not        effected by phases present, gas flow, temperature and humidity.        The solid carbon dioxide-substrate-atmospheric system is fairly        invisible to the photons and therefore do not hinder the        ionization effect.    -   6) The photoionization effect works instantaneously upon the        submicron particles held on surfaces, delivering significant        energy to the surface-particle region—breaking strong        electrostatic energy bonds instantly.    -   7) During application of snow particles—the contact interface        where the particle meets the substrate is continuously bombarded        with ionizing radiation (the radiation passes through the snow        particle). This eliminates the tribocharging effect during        creation. This provides a photoelectric antistatic agent at the        solid particle-substrate interface without chemical        contamination.    -   8) The photoionization effect with the device can be tuned to        work on all shapes, sizes and compositions of substrates—the        photoionizer produces a 120 degree cone of ionization. The        closer the photoionizer, the more focused and faster the        ionization effect (higher density of photons). During sublimable        spray operations, the photoionizer is focused (small area        radiation) primarily on the contact zone. During pre- and        post-cleaning operations, the photoionizer is in a defocused        (large area radiation) orientation.

Turning to FIG. 12, there is shown a diode laser integrated with theapplicator The diode laser (320) and spray applicator (322) are mountedon a common manifold (324). The manifold (324) contains a diode laserpivot (326) and spray applicator pivot (328) for adjusting the alignmentof each device with respect to the contact cleaning point on thesubstrate (330). The cleaning manifold to connected to a multi-axisrobot (not shown) using a robotic mount (332). Connecting the manifoldto a multiaxis robot provides for any number of possible orientationsand angles as shown graphically. The diode laser is tunable to provideboth spot and broad-spectrum substrate heating—the robot provides thefocusing control for both the spray applicator and diode laser. Anotherfeature shown in the figure is a spin processor (334). The spinprocessor holds the substrate under vacuum (336) via a vacuum chuck(338). The substrate is spun at a rotational velocity of between 20 and5000 rpm. The laser cleaning manifold is scanned from the interior (asshown) to the perimeter of the substrate while the substrate is spinningbelow. Software is used to control the pressure, temperature and diodelaser process sequencing. One possible process using the presentembodiment involves decreasing propellant gas pressure while themanifold moves from the interior region (lowest centripetal force) tothe perimeter (highest centripetal force). Using this approach, theactual impact force (cleaning energy) of the stream is continuouslydecreased to compensate for the increasing centripetal force toward theperimeter—providing consistent cleaning energy across the entiresubstrate. Another process involves using the diode laser to preheat theentire substrate at a defocused distance above the substrate. The robotthen moves the entire applicator manifold to the focused position forintense lasing during cleaning. Finally, the photon-process is performedin a laser shielding box (340) to protect workers from exposure. Lasershielding may be constructed of many materials having suitable IR laserabsorbing/reflecting properties such as stainless steel or speciallycoated polymers and glasses.

The preferred wavelength for the diode laser used in the presentembodiment is about 940 nm. This wavelength is invisible to solid carbondioxide, allowing the snow spray cleaning operation to be performedsimultaneous with the lasing operation with no impact on eitherapplicator's performance. When used during snow cleaning, the nearinfrared laser operates predominantly on the substrate at the snowcleaning contact point and above—water vapor on and within atmosphereabove the contact point. Moreover, the snow spray is an excellentcoolant for the laser, preventing overheating of delicate substrates.

Combining cleaning with many industrial, semiconductor, microelectronicor disk drive manufacturing processes dramatically minimizes productiontimes, superior process control, reduces consumables costs, andeliminates the need for separate production equipment such as solderingsystems, stripping systems, curing ovens, thermal treatment systems,cool-down times and adhesive application systems. Representativeprocesses include:

-   -   cleaning to pretreat substrates prior to Laser microwelding of        metals.    -   cleaning to pretreat substrates prior to application of adhesive        prior to Laser thermal cure.    -   cleaning to pretreat substrates prior to Laser soldering.    -   Laser-induced pyrolysis of coatings prior to ablation to reduce        stiction or adhesion.    -   Laser-induced excitation of boundary layer particles prior to        ablation to reduce intermolecular adhesive force.    -   Laser-induced heating during cleaning to prevent substrate        cooling.    -   Laser-induced heating prior to or following cleaning.    -   Laser drying of wet substrates prior to cleaning.    -   Laser removal of demarcations prior to cleaning.    -   Simultaneous cooling during soldering or joining to protect        sensitive components from heat.    -   providing a rapid cooling following thermal joining.    -   Laser wire stripping and cleaning.        Advantages of this inventive embodiment include:    -   Multiple integration options—cleaning, cutting, soldering,        joining curing and cooling.    -   Fiber optically coupled diode laser does far less collateral        damage as compared to Xenon Flash lamp-Pellet approaches such as        in the Boeing Flashjet Approach.    -   Designed for microelectromechanical applications as compared to        the Boeing FlashJet approach (removal of coatings from aircraft        wings and bodies using a flashlamp and low velocity pellets).        cleaning applies to cleaning miniature surfaces such as        head-gimbal assemblies (HGAs), quartz sensors, fiber optic        lenses and quartz resonators.    -   Laser is generally line-of-sight cleaning for planar substrates        under highly controlled conditions, such as the Radiance        approach, while the Diode Laser-approach can be applied to much        more complicated topography with a generally less controlled        approach. Diode lasers are not wavelength specific and provide a        general purpose intense heat source. There is no need for        focusing lenses, steering mirrors and the customized and complex        and system/application-specific configurations (tooling)        necessary for each type of substrate. The present invention        teaches the use of robotic focusing (working distance to        substrate) to control energy delivery.    -   Moreover, ultraviolet excimer lasers (KrF—248 nm), C02, and        Nd:YAG lasers used by the Radiance system are used to produce        photon flux to break bonds holding contaminants which are then        swept away in a laminar gas flow stream above the substrate.    -   Compact size, high efficiency, low cost in mass production,        high-power, fiber-coupled, diode laser arrays are a very good        alternative to C0₂ and Nd:YAG lasers in laser material        processing applications.    -   Coupling the systems to a 5-axis robot and software provides an        articulated and integrated production tool. Packaging this        production tool in a minienvironment provides a        microcontamination-free production tool. Multi-axis robots        manage the substrates providing a completely automated        (lights-out) production tool.    -   Combining LASER and dry cleaning technologies provides an        alternative to expensive and hazardous alternatives. This        process eliminates water in the cleaning process that can be        several 100 gallons of expensive deionized water of        approximately 2000 gallons used in typical semiconductor wafer        production cycle. The present embodiment also eliminates        reprocessing and disposal costs, eliminates the need for alcohol        drying and eliminates secondary reactions such as oxidation,        ionic contamination, corrosion and bacterial growth.    -   The inventive embodiment removes contaminants that cannot be        removed using conventional snow cleaning techniques.

This inventive embodiment simultaneously heats a substrate duringcleaning which prevents a thin film of water ice from forming on thesurface of the substrate—encapsulating contaminants in a 300 psi tensilestrength sheet of ice. Furthermore, the substrate exits the process ator above ambient temperature which prevents re-deposition of vapor phaseand particulate contaminants.

Referring to FIG. 13, there is shown a robot-based integrated cleaningsystem and process simultaneously using the spray cleaning, laserheating and photoionization embodiments of the present invention. Asshown in the figure, the substrate to be cleaned is a semiconductorwafer (342) mounted on a spin processor (344). The wafer is spun to aspeed of between 50 and 5000 rpm. The integrated cleaning tool comprisesa diode laser tense (346) which is fiber optically connected to ainfrared laser light generator and controller (not shown), a Snow sprayapplicator (348) which is connected coaxially connected to a generator(not shown), and a photoionization device (350) which connected to aphotoionization power supply (not shown). The integrated cleaning toolis further integrated on a common manifold (352) which is connected viaa robotic mount (354) to a cartesian robot (not shown). In Step 1 asshown, the integrated cleaning tool is robotically positioned above thesubstrate at the center of the substrate in the defocused position (356)wherein the diode laser beam is turned on and is irradiating a broadsection of the spinning substrate with infrared radiation (360). Thephotoionization device is also turned on and is irraditating a broadsection of the substrate with ionizing photons (362). In Step 2 asshown, the integrated cleaning tool is positioned in a focused positionat the center of the substrate (364). In this position, both the diodelaser beam (366) and photoionization beam (368) are in the highlyenergetic focused position. In Step 3 as shown, the substrate is scannedfrom the center (370) to the perimeter (372) any number of times toprepare the substrate for cleaning by drying, heating and ionizing thesubstrate. The temperature of the substrate may be preheated to anytemperature between 20 C and 300 C during this substrate preparationstep. A described herein, the use of the diode laser is varied and canbe for drying substrates, heating substrates, welding or joining. Inthis particular example, the laser is used to remove water and preheatthe substrate. In Steps 4 and 5 as shown, the spray applicator is turnedon (374) and all three devices are used simultaneously to clean thesubstrate any number of times by scanning from the center (376) to theperimeter (378) of the spinning substrate. In Step 6, the spray isstopped, leaving the diode laser and photoionizer on, whereby in Step 7the integrated cleaning tool is repositioned above the center of thesubstrate in the defocused position (380) using the robot (not shown).In Step 8, the integrated tool is scanned in the defocused position fromthe center (382) to the perimeter (384) of the spinning substrate toheat the substrate above ambient temperature. In Step 9, an infraredthermometer (386) is used to determine the temperature endpoint for Step8. The substrate is dry, clean, ionized and hot (388) following Steps 1through 9.

FIG. 14 shows a robotic cleaning workstation in accordance with thepresent invention. As shown in the figure, Top View, the roboticcleaning workstation contains a multiaxis substrate transfer robot, suchas a Mitsubishi RV-M2, at the center and shown in four positions—loadingplatform position (390), cleaning platform position (392), inspectionplatform position (394) and offloading platform position (396). Dirtysubstrates are loaded into the loading platform position, a door isclosed (not shown), and the transfer robot picks up a substrate (398)from a fixture (400) located in the loading zone using an end-effector(402) such as a vacuum grip. The substrate is then transferred to thecleaning platform and placed onto a vacuum spin processor (404) that isintegrated to a cartesian robot (406) such as a Sony DeskTop Robot. Thecleaning applicator—a manifolded diode laser, spray applicator andphotoionizer (408)—is affixed to the cleaning robot and can be moved inany Cartesian direction X-Y-Z and the manifold can be rotated from anyoffset angle from 0 to 45 degrees from normal over the spinningsubstrate (410). The substrate cleaning process described above usingFIG. 13 is then performed. Following cleaning, the transfer robot picksup the substrate and transfers the substrate to the inspection platform(412). The inspection platform comprises an inspection robot (414) suchas a Sony Desktop Robot that is integrated with the OSSE surfaceanalysis sensor (416) embodiment. The inspection robot can be moved inany cartesian direction X-Y-Z and the inspection sensor can be rotatedfrom any offset angle from 0 to 45 degrees from normal over thesubstrate (418). The inspection sensor (416) is used to scan thesubstrate surface at a predetermined distance and surface inspectionpattern to discern molecular contamination remaining following cleaning.Alternatively, the inspection sensor may be a video camera for visualinspection of substrate features. Following inspection, data gatheringand analysis, the substrate cleanliness is either accepted or rejectedusing computer analysis software. Unacceptable cleanliness requires thesubstrate (418) to be recleaned. The transfer robot picks up thesubstrate and places the substrate onto a holding platform (420) if thecleaning platform (404) is occupied with another substrate, or returnsthe substrate back to the cleaning platform for recleaning. Followinginspection and acceptance, the transfer robot picks up the substrate(418) and transfers the substrate to the offloading platform (422) wherethe cleaned and inspected substrates (424) are collected for unloadingfrom the workstation.

Also shown in the Top View of FIG. 14 are the basic design features ofthe workstation. These include a fully enclosed housing (426)constructed of stainless steel, acrylic or other suitable materials forusing the present embodiments—1) safe-guarding workers from exposure tox-rays, laser radiation and carbon dioxide gas and 2) safe-guarding thecleaning environment within the enclosure from external environmentalelements such as moisture and particles. The workstation contains avertical laminar flow ULPA filtration system (428) and a raised floorgrating (430) for recirculating internal atmosphere. A computer console(432) is affixed to the outside of the workstation for operator inputand cleaning process output. The computer console contains a means forprogramming the various robots used in the present embodiment and forinputing cleaning and inspection criteria. Finally, a printer (notshown) may be integrated with the computer console for producing printedreports following each completed cleaning process cycle. Substrates arefed into the workstation using a loading dock (434) which may contain asliding door (not shown) and substrates are withdrawn from theworkstation using an unloading dock (436) which may contain a slidingdoor (not shown).

Shown in the Side View of FIG. 14 are above-described and additionalfeatures of the workstation. A lightstack assembly (438) is used toprovide a visual operational status for the workstation (i.e.,Red-Operating, Green-Not Operating). All satellite systems including theCleaning System, Robot Control Systems, Fluids Management System,Accessory Control Systems and Input/Output and Power Control System arelocated within a control bay (440) located in the lower hemisphere ofthe workstation and isolated from the cleaning and inspection bay (442)located in the upper hemisphere of the workstation. Fluid input (gaseouscarbon dioxide), ventilation duct and electrical power connections aremade toward the rear of the control bay as shown in the figure. Anatmospheric management bay (444) located in the central hemisphere ofthe workstation integrates the floor grating (430) via a common ductingsystem (446) to an environmental control system (448) and the ULPAfilter system (428). As shown in the figure using arrows, the internalworkstation atmosphere is recirculated from the cleaning and inspectionbay (442) down through a raised floor grating (430), into theenvironmental control system (448), into the ULPA filter system (428)and back into the cleaning and inspection bay (442). The environmentalcontrol system (448) comprises a regenerating gas dryer (i.e., metaloxide) and heater (both not shown). Using a thermometer and humiditysensor (both not shown) located within the cleaning and inspection bay,the environmental control system maintains the cleaning and inspectionbay temperature and humidity at predetermined settings. Duringregeneration operations, the gas dryer is heated to 200 C and dry carbondioxide gas is used to purge moisture from the dryer which is ventedfrom the workstation. Optionally, the ULPA filter system (428) maycontain ionization bars (not shown) affixed to the downstream side ofthe filter to provide internal ionization of the cleaning and inspectionbay.

The entire cleaning process performed within the workstation isautomated and controlled using system software in combination with a PCor PLC, various electronic switches, digital controlled pressure andtemperature controllers, a robot, a photoemission inspection system andlaser system. The system software is written for Visual Basic operatingon a Windows NT and using an Allen Bradley PLC controller. The presentsystem software embodiment teaches in-situ correlation betweenphotoemission analysis and cleaning performance with automatic snowpressure and temperature adjustments. The system software also teachesan internet-based preventive maintenance code block within the softwareto perform remote system diagnostics and repair.

FIG. 15 shows the computer and software-based control systemarchitecture for automatically operating the various embodiments of thepresent invention. A main control system (450) comprising a centralcomputer system, programmable logic controller and software is used toprovide all input-output management of the cleaning process and system(452), inspection process and system (454), environmental control system(456), fluids management system (458) and robot controllers (460). Therobot controllers include the transfer, cleaning and inspection robots.The robots each have typically three components. For example thetransfer robot system (462) comprises 1) a teach pendant to teachpositions to the robot to execute the four pick and place operationswithin the workstation, 2) a robot controller to store taught positionsand to interface with the main control system (450) and 3) a multiaxisrobot containing an vacuum grip end-effector (464) or in the case of thecleaning and inspection robots—cleaning and inspection end-effectortools.

Operational software is used to manage and operate the various systemsdescribed herein. The computer software displays a graphical interfaceto the user, accepts inputs for a variety of process parameters anddisplays various system outputs.

Below are exemplary process inputs:

Cleaning Process Parameters:

-   -   EJTCR Injection Feedrate    -   Propellant Gas Temperature    -   Propellant Gas Pressure    -   Ionization Power Supply    -   Pulsed or Continuous Operation    -   Pulse Rate    -   Additive Injection    -   Additive Injection Feedrate    -   LASER System    -   LASER Pointer    -   LASER Power    -   Photoionizer System    -   Spin Processor System    -   Spin Processor Speed    -   Print Report (Yes/No)        Transfer Robot Parameters—Pick and Place Operational Recipes:    -   Load—Clean Positions    -   Clean—Inspect Positions    -   Inspect—Reject Positions    -   Reject—Clean Positions    -   Inspect—Unload Positions    -   Grip/Ungrip Positions    -   Transfer Speed        Cleaning Robot Parameters—Manifold Operational Recipes:    -   Starting Position(s)    -   Ending Position(s)    -   Focused Position(s)    -   Defocused Positions(s)    -   Offset Angles(s)    -   Scanrate    -   Number of Scans        Inspection Robot Parameters—Sensor Operational Recipes:    -   Starting Position(s)    -   Ending Position(s)    -   Focused Position(s)    -   Defocused Positions(s)    -   Offset Angles(s)    -   Scanning Rate    -   Number of Scans    -   Acceptance/Rejection Criteria    -   Print Report (Yes/No)

Below are exemplary process outputs:

Stream System:

-   -   Fluid Temperatures    -   Fluid Pressures    -   Fluid State (Gas/Liquid)    -   System Status        Robot Systems:    -   Cartesian Space Positions    -   Robot Status    -   Grip Status    -   Speed    -   Sequence        Environmental Control System:    -   Temperature    -   Humidity    -   Regeneration Sequences        Fluids Management System:    -   Temperature    -   Pressure Phase    -   Supply Level (Optical Sensor)        Inspection System:    -   Analysis and Results

Using the transfer robot system (462) and teach pendant (466), the userteaches the transfer robot the substrate transfer operations which movethe substrate from the load position, through the cleaning andinspection positions (and holding position), and finally to. the unloadposition—called pick and place operations (468). Following this, theuser inputs the leaning process parameters (452) and inspection processparameters (454) given above into the computer, including pass/failanalysis criteria (470) for the inspection process. Following this, theuser has constructed a cleaning process recipe which can be saved as aunique process filename for future reference and repeatability. Theprogram may then be started (472), whereupon the entire cleaning processrecipe, including robotics, cleaning and inspection criteria, isexecuted sequentially until completion (474).

Finally, the system software is designed with capability to communicateto a factory process management system through an Ethernet connection(476). Moreover, the software is designed to allow a service supporttechnician to remotely diagnose system operation and function over theinternet (478).

FIG. 16 shows the cryogenic microabrasive surface finishing apparatusand process embodiment of the present invention. Machined or moldedpolymeric substrates often contain plastic burrs around various edgesand surfaces. Removal of burrs using conventional deburring usingmicroabrasives does not always produce an acceptable surface because theburr tends to fold over during ablation. The present process provides ameans for producing ultrafine abrasive finishing by supercooling theburr, with respect to the substrate, thereby making the burr hard andbrittle. Impact by an abrasive under these conditions produces a cleanand fast separation because the burr temperature drops much faster thanthe substrate temperature.

The cryogenic abrasive finishing apparatus consists of a abrasivecleaning applicator (480) with the propellant gas supply (482)containing microabrasives fed down the coaxial delivery line (484).Dense snow particles are fed down a centrally located snow tube (486)from the EJTCR loop (488). The two streams are integrated at a distancefrom the abrasive cleaning applicator (480) using a tee connection(490). Any number of abrasives as shown may be employed in the presentembodiment.

The abrasive cleaning process is performed as shown and described asfollows. A substrate containing small edge burrs (492) is showered withan abrasive spray stream (494), with the propellant gas heater turnedoff. Following this, the propellant gas heater is activated and themicroabrasive injection device (not shown) is deactivated—showering thesubstrate with a cleaning spray stream (496). The substrate (498) is nowfinished and clean.

The present invention provides capabilities not found in conventionalsnow cleaning technology. The following is an cleaning and productionapplication wherein the present invention is used to provide integratedmultiple cleaning operations during assembly, provide a thermal curingprocess and dynamically alter snow spray cleaning energy duringapplication where the substrate contains mechanically sensitive featuresthat require the cleaning spray to have a lower spray pressure in onearea and possibly an increased cleaning spray energy in other areas. Thefollowing example is only one of many integrated substrate cleaning,production and assembly operations possible using the present invention.

As shown in FIG. 17, the substrate—a small electronic chip or die(500)—is electrically connected to an electronic module (502) using anynumber of microscopic wires (504). The die is placed onto the electronicmodule and bonded into place. The spray cleaning processes of thepresent invention are used to clean the bonding surfaces of module (502)for the initial die placement and bonding operation. Following theinitial die placement, microscopic wires (504) are placed—joining theelectronic connections on the die (506) to the electronic connections onthe module (508). In the application, the interconnection bondingsurfaces are cleaned using the present invention prior to dispensing asmall droplet of a heat curing conductive adhesive (i.e., silver-filledepoxy). Following cleaning and adhesive placement, the small wires arerobotically placed into each epoxy solder joint Following this, thediode laser embodiment of the present invention is used to rapidly andthermally cure the epoxy joints. A final spray cleaning is performedusing the present invention to remove any residual particles followingdie bonding, adhesive placement, wire bonding and curing operations andprior to lid placement. The spray pressure is dynamically controlled toproduce a much lower spray pressure in the regions near the wires. Asshown in the figure, the spray pressure is decreased from 80 psi (510),to 50 psi (512) and finally to 30 psi (514) as the spray applicator(indicated as arrows) approaches the mechanically sensitive wire bondingareas.

1. A dense fluid spray cleaning apparatus for producing a streamcontaining a solid particulate comprising: a dense fluid propellantgenerator fluidly connected to a dense fluid supply for producing aheated, dense fluid propellant; an Enhanced Joule-Thompson CondensationReactor fluidly connected to a dense fluid supply for producing a solidparticulate from the dense fluid; a premixer for indirectly mixing theheated, dense fluid propellant received from the propellant generatorand the solid particulate received from the enhanced Joule-ThompsonCondensation Reactor, the premixer including inner and outer coaxialtubes, the inner coaxial tube in fluid connection with the EnhancedJoule-Thompson Condensation Reactor and the outer coaxial tube in fluidconnection with the dense fluid propellant generator; and a mixer fordirectly mixing the heated dense fluid propellant and the solidparticles received from a premix chamber to produce a stream containingthe solid particulates.
 2. The apparatus of claim 1 wherein the densefluid propellant generator includes a dense fluid ionizer.
 3. Theapparatus of claim 1 wherein the Enhanced Joule-Thompson CondensationReactor includes a spray nozzle and a loop, such that the spray nozzleinjects dense fluid received from the dense fluid supply into the loop.4. The apparatus of claim 3 wherein the loop has a length of from about6 inches to about 20 feet, an outer diameter of from about 1/32 inch toabout ⅛ inch, and an inner diameter of from about 0.0025 inch to about0.80 inch.
 5. The apparatus of claim 3 wherein the loop has a length offrom about four feet to about five feet, an outer diameter of from about1/32 inch to about ⅛ inch, and an inner diameter of from about 0.02 inchto about 0.80 inch.
 6. The apparatus of claim 3 wherein the loop is madeof polyetheretherketone tubing.
 7. The apparatus of claim 6 wherein thepolyetheretherketone tubing is first overlapped with a groundedconductive shielding and then overlapped with a thermally insulativematerial.
 8. A method for producing a spray cleaning stream containing asolid particulate formed from a dense fluid comprising: producing aheated, dense fluid propellant; producing the solid particulate from adense fluid using an Enhanced Joule-Thompson Condensation Reactor;indirectly mixing the heated, dense fluid propellant and the solidparticulate in a premix chamber having inner and outer coaxial tubes,the inner coaxial tube for transporting the solid particulate and theouter coaxial tube for transporting the dense fluid propellant; anddirectly mixing the heated dense fluid propellant and the solidparticulate received from the premix chamber to produce the spraycleaning stream containing the solid particulate.
 9. The method of claim8 wherein the solid particulate is made of carbon dioxide.
 10. Themethod of claim 9 wherein the dense fluid propellant has a temperatureof from 70 F. to 300 F.
 11. The method of claim 9 wherein the densefluid propellant is ionized.
 12. The method of claim 9 wherein the densefluid propellant contains a solid abrasive.
 13. The method of claim 9wherein the solid particulate has a size from 100 micrometers to 0.2micrometers.